This invention relates primarily to protective devices for use with and for the prevention of damage to the electrical components of key telephone systems. I am aware that a U.S. patent application, Ser. No. 811,293, filed June 29, 1977, is co-pending with mine covering various forms of related devices which it is my understanding will be assigned to Bell Laboratories of Holmdel, New Jersey and Illinois Tool Works Inc. of Chicago, Illinois, the latter being the assignee of this present invention.
Several years ago, telephone companies replaced mechanical relays in key systems with printed circuit boards and semiconductors; this change caused a sporadic rash of circuit failures. A solution to the problem is to install a bleeder resistor from the ring control circuit to a permanent ground. The most feasible place to utilize such a bleeder resistor is in the intermediate terminal blocks utilized on the key telephone relay equipment itself and/or at multiple phone installation interconnecting blocks. Such blocks consist of rows of terminals that are flat, split beam members adapted to accept wire conductors between the split portions of each terminal. It was found that if the resistor connections were pressed into the split terminal, the integrity of the connection to the existing conductor was jeopardized. To wind the lead around the terminal was time consuming and too permanent. An attempt was then made to solder spade terminals to the resistor leads, encapsulate them in epoxy, and apply the spade terminals to the upright split terminals mounted in the terminal block. This was found to be too bulky and prone to being knocked off the terminal board.
A secondary problem exists in that such terminal blocks consist of rows of edge-to-edge terminals with the spacing between adjacent rows varying between different types of blocks used for different sizes of installations. This requires adaptability of connector means for acceptance by a multiplicity of spacings in the rows between terminals in such blocks.
A further problem incurred in the usage of terminal blocks in communication systems is the interruption of service by a serviceman while a call or function is in progress. The use of a warning device to prevent the serviceman from accidentally interrupting a circuit has been found desirable.